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Last updated on Oct-18-2019 Download

SNROM nightmare

SNROM nightmare
by on (#76231)
I've been trying to build a simple SNROM devcart for several months now; my attempts have become more and more discouraging and slowed me down a lot. I thought I'd been using the right instructions, at least the only one that seens to exist right now. I'm using a Pm29F002T-12PC; a 2 megabit Flash ROM. the EPROM conversions seem to make sense, the pinouts seem to be the same as for a standard 2 Mbit EPROM and I've made sure the correct data is on the chip.

4 of my favorite games (not rare, at least) have now been destroyed for all my efforts. I figured when I finally succeed with one I will know what is required and maybe notice something I had previously missed with the others enabling me to fix them, but as of yet I've had abysmal luck.

has anyone else had problems building an SNROM cart? is there something obvious that I'm perhaps missing? I've made sure WE# is pulled high and CE# and OE# are pulled low, all that sort of stuff, and there were only two address pins re-routed which I've been very careful about.

somebody please tell me what I'm doing wrong!

by on (#76235)
Curious as to why you're not using a PowerPak for development then. Mine actually was DOA, but after some finangling I got it repaired by RetroUSB. I suggest you get one of those instead, will probably save you money, energy and heartache.

by on (#76240)
ManicGenius wrote:
Curious as to why you're not using a PowerPak for development then...I suggest you get one of those instead, will probably save you money, energy and heartache.


but I don't mind spending that, as long as they eventually work. Building a devcart hasn't proven to be irredeemably stressful yet. I want to have a handful of devcarts at my disposal as opposed to one super-versatile one.

E.g. If I want to run 3 separate NES animations at one time I'd rather not order 3 PowerPaks just for this purpose, or if I want to play 2 or more NES music tracks over each other and switch them physically, without a menu etc...

and please don't suggest emulation :-|

another advantage of being able to make one out of a very common game is that I could distribute homebrew programs to people, and give them as gifts.

by on (#76241)
See if you can come by a bunch of Ultima Exodus games for cheap.

by on (#76242)
tepples wrote:
See if you can come by a bunch of Ultima Exodus games for cheap.


I have a copy. and it's next in line for operation aka "on death row"...unless I see the problem and fix it before that

by on (#76244)
Roni wrote:
and please don't suggest emulation :-|


Wouldn't dream of it. I do a typical dev cycle of a couple hours of rapid dev/test with emulators. Then a final night test on real hardware with the PowerPak. Saves me the effort of erasing/burning flash chips. Hardware testing is the final kick in the nuts for something like this.

As for distributing SNROM, grab a RetroUSB PCB. $9 as far as I can tell. Though I can't speak for them since I haven't used that yet and my game uses UNROM (and thus I save $5).

by on (#76245)
I have found that these instructions don't tell you everything, its been a while since I made a cart. I do recall having to bend up pin 32 on PRG as well as connecting pin 1-32-31 together on one or more of my carts. Try this out see if it helps.

by on (#76246)
ManicGenius wrote:
Roni wrote:
and please don't suggest emulation :-|

...As for distributing SNROM, grab a RetroUSB PCB. $9 as far as I can tell...


but I'd still have to desolder a lockout chip or order one, not to mention a case, and supplies of NES carts are still plentiful.

all that's required to make a devcart is a donor cart, a compatible ROM chip, possibly a DIP socket and the right method...it's the latter which eludes me right now.

by on (#76252)
Eh... it's probably the collector in me that hates cannibalizing perfectly good games, unless the game is something I care absolutely nothing about like NFL '89.

As far as lock-out chips are concerned, you really should snip that. Nothing better in the world than dealing with an uppity NES that immediately runs better after being neutered. Calms the hell down just like a Rottweiler.

by on (#76255)
CIC neutering is not possible when I'm sending someone something and telling them to "just pop it into your NES and turn it on". anything more complicated than that defeats the purpose.

by on (#76256)
RetroZone also sells a CIC replacement chip, the CIClone, which works on all consoles.

I am building an SNROM dev cart myself (parts should be in tomorrow, I am SO excited :D) out of parts from RetroZone. I decided against canabilizing an Ultima Exodus cart because I thought all the pin bending was a bit too much hassle.

Here's the thread where we discussed it. See the unfinished Wiki Page for an accurate parts inventory.

After I have assembled and tested the cart I will complete the Wiki page with instructions.

by on (#76257)
The instructions say to bend up pin 31, but then what? It doesn't say. That pin is the /write signal on the pm29f002t. For read-only operation it must be connected to VCC. I'm not sure what an EPROM would do if that pin was left unconnected, but I'd expect a flash chip wouldn't work. It might think it's being written to, and/or going into command mode.

If you can find an AT29C256 (32kB), you can use those with NROM and CNROM boards without any rewiring. Then burn the program onto an OTP 27C256 or 27C512 if/when you're done editing it.

by on (#76258)
qbradq wrote:
RetroZone also sells a CIC replacement chip, the CIClone, which works on all consoles.

once again I have no plans to order an MMC1 repro board.

Quote:
See the unfinished Wiki Page for an accurate parts inventory.



checked it out. was immediately confused by the attitude that treats PowerPak as the norm and describes a devcart as if it were something obscure. *not approving*

by on (#76259)
Memblers wrote:
The instructions say to bend up pin 31, but then what? It doesn't say. That pin is the /write signal on the pm29f002t. For read-only operation it must be connected to VCC. I'm not sure what an EPROM would do if that pin was left unconnected, but I'd expect a flash chip wouldn't work. It might think it's being written to, and/or going into command mode.


Pin 31 is electrically connected to pin 32 on the cart so it is already connected to Vcc without any mod.

Quote:
If you can find an AT29C256 (32kB), you can use those with NROM and CNROM boards without any rewiring. Then burn the program onto an OTP 27C256 or 27C512 if/when you're done editing it.


I've already got NROM figured out and it's served its limited purpose for me. SNROM adheres to all the specs I need as well as the mapper I've decided on using regularly.

by on (#76260)
While this is here, may I suggest fixing the EPROM pinout diagrams? I about beat my head into a wall trying to find where to connect /CE onto a chip that only had CE to the tech docs on the main page. :wink: :roll:

by on (#76266)
Quote:
checked it out. was immediately confused by the attitude that treats PowerPak as the norm and describes a devcart as if it were something obscure. *not approving*


That wiki page is in response to those that treat the PowerPak as the norm. The PowerPak does not work on clone systems, which is not good for me.

I won't begrudge you not wanting to buy an MMC1 repro board. I'm sure you have your reasons. But I will mention that it is specifically designed to work with modern ROM and RAM chips, with no rewiring.

by on (#76269)
Do you have a multi-meter to check for shorted or open connections?

Only problem I had with my first rewired cart was some intermittent shorting of a bent-up pin. Putting electrical tape around it solved the problem. But if you can get a good cut (with an exacto knife or similar) I think it's better to cut the traces instead of bending the pins.

Sounds like your cart should work, only thing I can suggest is checking for bad connections, a continuity test.

by on (#76270)
I reviewed the datasheet for that ROM chip. It should be 100% compatible with what is in the document you linked to. Timing looks good too.

by on (#76278)
SUCCESS!!@!!!!!!1!1!!
okay memblers was on to something. it was the trace from 2 to 22 that I forgot to cut. the tutorials on Devcarting need to be seriously updated and I volunteer to help with that as soon as I'm done having fun.

by on (#76287)
I agree. First thing's first, though.....how about we fix the EPROM pinouts with the right enable, /CE, so people won't get confused there.

by on (#76290)
Roni wrote:
SUCCESS!!@!!!!!!1!1!!
okay memblers was on to something. it was the trace from 2 to 22 that I forgot to cut. the tutorials on Devcarting need to be seriously updated and I volunteer to help with that as soon as I'm done having fun.


I'm glad to see you got it going, I have always stayed away from trace cutting and preferred to rewire using cannibalized network cable. Once its all soldered and tested to work I use a little hot glue to hold it all neatly in place.